There are pros and cons of each of these cylinder types, but due to every system being different, there is no one answer about what type of cylinder is best. The question we really need to ask is which type of cylinder is best for your home. But before going into details about which type of cylinder is better for you, let’s have a look at exactly what each type of cylinder actually is.
What is a Vented Cylinder?
A vented cylinder, is a cylinder which is supplied by a cold water storage tank, usually found in your loft space, which fills the cylinder with cold water, before it is heated within the cylinder and then comes out hot at your taps. When the water in the tank is heated, the expansion caused by heating the water, is vented up through a vent pipe (hence why it is called a vented cylinder) back up and over the cold water tank. This type of cylinder is what is also sometimes called a “traditional” cylinder. They are usually copper and have an exposed foam insulation, to help keep the water hot for longer. These types of cylinders are usually found in older system and often, external pumps can be found near to the cylinder itself or near to bath/shower rooms.
What is a Unvented Cylinder?
An unvented cylinder, often mistaken just for a “Megflo”, is a hot water cylinder that is fed directly from the mains water supply. These are a more modern way of providing a store of hot water in homes and are often the preferred way of having a store of hot water. Because these types of cylinders are fed directly from the main and there is nowhere for the expansion to go when the water is heated, they all have some kind of expansion vessel fitted (this is instead of the vent pipe as mentioned in the previous paragraph). It also, due to the high pressure and temperatures that can build up in them, they have safety devices which help to release the build up of this pressure and overheating.
Why choose a Vented Cylinder?
There are a number of benefits to installing a vented hot water cylinder. A vented cylinder is a great solution if you have a poor incoming mains water supply, as you can then use external pumps to “boost” the water pressure to your bath/shower rooms. They also have the benefit, that if your mains water supply is turned off for whatever reason, that a store of water can still be used from the cold water storage tank whilst you are waiting for the mains water to be turned back on.
Are there any downsides to Vented Cylinders?
The main downside to vented hot water cylinders is the fact that you tend to get lower pressure and flow rate reaching your hot taps, without using a booster pump. The other downside to vented cylinders, is that by having the additional pumps and cold water tanks, they will also need maintaining and/or replacing periodically, adding to the cost and inconvenience of one of these systems. And lastly, the cold water storage tank can become contaminated and leave you potentially using unclean water to brush your teeth!
Why choose an Unvented Cylinder?
The benefits to installing an unvented hot water cylinder, are primarily that you are able to remove many of the additional components required in a vented cylinder installation, such as the storage tanks and booster pumps. This is due to the water being fed directly from the mains water supply. The downside to this type of cylinder, is that is you do not have the required amount of mains water flow rate and pressure, you will not get the desired amount of water flowing out of your taps. Put simply, if your incoming main is poor, your hot water supply will be poor. There are solutions to this, and in some properties (usually larger properties, where there might be three or more bath/shower rooms) it is possible to install a centralised booster pump in a plant room, for example.
Are there downsides to Unvented Cylinders?
The main downside to unvented cylinders, is that if your water supply is interrupted, your hot water is immediately also turned off. There is also, as mentioned above, the issue with needing a certain amount of flow rate and pressure for these cylinders to work effectively.
The other main downside to unvented cylinders, is the cost to both purchase and install these. A specific qualification, called a G3 qualification, is required to install and maintain these cylinders. Both of these factors increase the cost to have one of these cylinders installed.
The last downside to having one of these cylinders installed, particularly if you are replacing a vented cylinder, is that there needs to be a discharge pipe that runs from the cylinder, in copper pipe, directly to an outside wall, on a gradient and down to the ground (called a discharge pipe). When replacing a vented cylinder, it is common to find them on a landing cupboard, with no easy route to install a discharge pipe. This factor alone can add significant cost and complexity to installing one of these cylinders.
In summary
As no two systems are the same, in the same way that no two bodies are the same, each system has it’s own unique set of needs and challenges to face in order to get the most efficient use out of each system. When looking at what solution may be best for you, it is always best to get an experienced professional in to look at all of the variables and then advise you as to what is best for you.
We hope that this article has been of some use to you and if you would like to discuss your hot water options, please feel free to call us or leave a message in our contact form and we will be glad to help you! 
Telephone on local rate: 0207 137 3333 Email: hello@avenueheating.com
